This is the psychological bias that the more you know the less sure you are of yourself. People who would be considered experts know how much they don’t know and so are less sure of themselves, people who are not well versed in issue at hand will have greater confidence in being able to overcome the issue, simply because they are unaware of the large gaps in their knowledge.
President Trump is a perfect example of the Dunning-Kruger effect in action. Someone who is utterly convinced he can manage complex and difficult situations despite not having the necessary education, experience or understanding of the complexities involved.
It is important to understand that we all are all susceptible to this and many other biases and try and take this into account in our decision-making.